This invention relates to a dispenser of generic paste products, and in particular toothpaste, being of a type which comprises a cylindrical container having a vertical longitudinal axis, a headpiece provided with an output means for the paste product and located at the top end of the container, and a bottom wall arranged to slide in a tight manner inside the container in one direction toward the headpiece.
A dispenser of the same kind as specified above is described, for example, in European Patent Application No. 86830205.0-2308.
More particularly, the invention is concerned with the construction of the bottom wall, which is designed to close the container and, consequently to the pumping action exerted through the paste output means, to move up toward the headpiece while restrained from moving back down, thereby being effective to reduce the container volume by a corresponding amount to the volume of the dispensed paste.
It is known that such dispenser types are filled with their output mechanisms mounted to the headpiece by introducing the paste product through the open bottom of the container.
This bottom is then closed by fitting in the sliding wall.
That operation poses some problems when carried out, including problems of a mechanical as well as hydraulic nature, because at the time of fitting in the bottom wall attention should be paid to whether any air is trapped in between the paste introduced into the container and the bottom wall. This air must be thoroughly removed.
It is, in fact, only in the total absence of air that the bottom wall can be made to intimately contact the paste all over and slide up the container by virtue of the pressure differential which is created at each dispensation between the outward side of the wall and the top of the column of paste inside the container.
After all the air has been vented out, however, the bottom wall is to both prevent the paste from seeping out and a fresh air cushion from forming, and therefore to provide an air-tight seal.
In accordance with a prior art approach, of which German Patent Application No. 3435576 is an example, the bottom wall is formed with an axial channel which opens both to the container inside and the outside, and a plug is pushed into the channel opening to shut it tightly after the container has been filled and trapped air vented out completely.
This prior approach apparently requires, however, that the bottom wall be pushed against the mass of toothpaste until the latter begins to overflow, in order to make sure that all the air has been removed and, accordingly, achieve an air-tight fit of the bottom wall.
In view of the characteristics of the automatic filling equipment employed, the detection of the exact moment when the air-tight fit can be correctly completed for the bottom wall involves a setup of checking arrangements and procedures which are bound to affect the product economy adversely.